Discovered: Monster solar system dwarfs our own

An international team of scientists has found a Godzilla solar system so extraordinarily large that one far-flung planet orbits its host star at the cracking distance of more than 1 trillion kilometres.

The gaseous giant, prosaically dubbed 2MASS J2126−8140, takes almost a million Earth years to orbit its star, which lies 100 light years away from us.

An artist's impression of the gas giant planet 2MASS J2126-8140 in orbit around its host star, faintly discernible in the background. Photo: Neil Cook, Hertfordshire University

"It's entirely possible that there's a more normal, familiar solar system also orbiting around the host star," Dr Murphy explained. "But the new planet would not have formed in the same way as our solar system did, from a large disc of dust and gas."

The new planet is so far out - its orbit is more than 140 times wider than that of the dwarf planet Pluto - that it would have little or no impact on the evolution of other planets lying closer to their parent star, if they exist.

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The parent is a red dwarf, a small star that is relatively cool. "Unlike most red dwarfs, this star is very young," Dr Murphy said.

Stars like this are generally more active and energetic than the Sun. "So it's possible any planets would have been impacted by flares and mass ejections from the star over the past 10 to 45 million years," he explained.

Only a handful of planets orbiting at mind-numbing distances from their host stars have been detected.

The distances are so great that they are measured in astronomical units, the average distance of about 150 million kilometres between the Sun and Earth.

By comparison, Pluto orbits the Sun at an average distance of 40 astronomical units. The recently reported ninth planet, a giant icy world several times larger than Earth, orbits at more than 200 units.

It's entirely possible that there's a more normal, familiar solar system also orbiting around the host star.

"At that distance, it would appear as only a moderately bright star in the sky – its light taking about a month to reach the planet," Dr Murphy said.

"Once we realised that the star and planet were a similar distance from the Earth – about 100 light years – we compared the motion of the two through space and realised they were moving together," he explained.

Astrophysicists speculate they formed 10 million to 45 million years ago from a filament of gas that pushed them together in the same direction.

"They would not have lived their lives in a very dense environment," Dr Murphy said. "They are so tenuously bound together that any nearby star would have disrupted their orbit completely."

The research, currently in preprint, will be published next month in the respected journal, Monthly Notices of the Royal Astronomical Society.